To understand the nature of virushost interactions at sea, Sallie Chisholm and colleagues sequenced three marine phages - one podovirus and two myoviruses - based on their morphology and host range, and characterized their genomes. The marine phages resemble two terrestrial phages - called T4 and T7 - that infect Escherichia coli but also carry genes that appear specially adapted to infecting photosynthetic bacteria in nutrient-poor oceans. Some genes are likely derived from cyanobacteria that "could play defining functional roles" in marine phagehost interactions. All three cyanophages contain photosynthesis-related genes, some of which could mean that the virus helps the host maintain photosynthesis during infection. The podovirus also has a candidate gene involved in DNA synthesis, which the authors speculate could allow the virus to reproduce in nutrient-poor environments, and all three cyanophages carry genes involved in metabolizing carbon. The absence of such genes in terrestrial phages, the authors argue, lends support to the notion that marine phages have evolved different adaptive mechanisms in response to the ocean environment.
Given the intimate relation between virus and host, the effects of gene swapping between virus and host is likely to b
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